1. Field of Invention
The present invention relates to the measurement of scattering parameters for microwave and radio-frequency (RF) devices-under-test (DUTs) under nonlinear operating conditions.
2. Description of the Related Art
It was shown in J. Verspecht, M. Vanden Bossche and Frans Verbeyst, “Characterizing Components Under Large Signal Excitation: Defining Sensible ‘Large Signal S-Parameters’?!,” 49th ARFTG Conference Digest, pp. 109–117, June 1997 that the nonlinear behaviour of a radio-frequency or microwave device-under-test with a periodic excitation signal at the input in a near matched environment can accurately be described by a ‘Large-Signal S-parameter’ model as defined in the above reference.
One practical method to measure the ‘Large-Signal S-parameter’ model for an actual DUT, restricted to fundamental frequency behaviour only, is described in Frans Verbeyst and Jan Verspecht, “Characterizing non-linear behavior,” European Patent Application “EP 1 296 149 A1”. With this method the ‘Large-Signal S-parameter’ model is identified by connecting to the output port of the DUT a matched load, an open, a short and a plurality of attenuators and delays and by each time measuring the fundamental spectral component of the incident and scattered voltage waves. The ‘Large-Signal S-parameters’ are then calculated by digitally processing the acquired data.
In Jon S. Martens, “Probe Tone S-parameter Measurements,” United States patent application Publication, Pub. No.: “US 2002/0196033 A1”, is described how ‘Hot S22’, which is one part of the complete ‘Large-Signal S-parameter’ model, can be measured by using a frequency-offset probe-tone method. With this probe-tone method a one-tone excitation signal is applied at the input signal port of the DUT (this is called the “power tone”, its frequency is called the fundamental frequency), while a small one-tone signal with a frequency equal to the “power tone” frequency plus a small frequency offset is applied at the output signal port of the DUT (this signal is called the “probe tone”). ‘Hot S22’ is calculated by taking the ratio between the measured reflected voltage wave at the output signal port having a frequency equal to the fundamental frequency plus the said frequency offset and the measured incident scattered voltage wave at the output signal port having a frequency equal to the fundamental frequency plus the said frequency offset.